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    A Study of the Reproducibility of the Micro-Vac Technique As A Tool for the Assessment of Surface Contamination in Buildings with Asbestos-Containing Materials

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    The Standard Test Method for Microvacuum Sampling and Indirect Analysis of Dust by Transmission Electron Microscopy for Asbestos Structure Number Concentrations (D-5755-95) was balloted and passed in 1995. Estimates of the precision of this method was determined by examining historical data from a round robin laboratory study and as actual dust samples taken from buildings with asbestos fireproofing. The analysis followed the draft ASTM dust method that was in use at that time. Like most ASTM methods, the development of the D-5755-95 method involved a series of draft methods, each differing somewhat from its predecessor. While some changes were made to each draft, these changes were primarily made to the sample preparation and analysis sections of the method. No changes were made to the sections addressing sample collection. Since the dust sample data was generated using several draft methods and the final method, the differences between methods may have contributed to the data's variation. The first study consisted of dust samples that were sent to nine independent laboratories. The laboratories involved in the round robin study were provided with known weight amounts of asbestos contaminated dust that was collected from a building with in-place vermiculitic asbestos-containing fireproofing. Good correlation was found between laboratories when the number concentrations were normalized to the weight amount of the dust provided to the labs. The round robin study demonstrated good precision with an overall coefficient of variation (CV) of 0.71. Several laboratories demonstrated a CV in the range of 0.30 to 0.40. These low CV values showed a high degree of reproducibility for the analytical method and indicated little if any numerical contribution from large particles (≤ 2mm) that may have been in some samples.

    A second study conducted from 1991 to 1996 examined a large database of dust samples that were collected from 38 buildings located throughout the United States. These buildings also contained a vermiculitic asbestos-containing fireproofing product. The samples were collected from surfaces beneath the fireproofing. No physical barriers or obstructions were present between the fireproofing and the surface sampled. Only buildings with at least three or more collected samples were included in the study. These sample sets were selected to control variation due to sample location, collection technique and type of asbestos-containing material (ACM) present. While samples collected within buildings did vary by more than one order of magnitude, statistical comparisons show a greater degree of variability between buildings than between samples collected within individual buildings. Additionally, this study showed good correlation with other similar data.

    The two studies showed that asbestos surface dust measurements determined by the micro-vac technique are reproducible and may be used to determine asbestos surface concentrations in buildings during asbestos evaluations.


    asbestos, analysis, dust, quantitative, round robin, buildings

    Author Information:

    Hatfield, R. L.
    Materials Analytical Services, Inc., Suwanee, Georgia

    Krewer, J. A.
    State of Georgia, Atlanta, Georgia

    Longo, W. E.
    Materials Analytical Services, Inc., Suwanee, Georgia

    Committee/Subcommittee: D22.07

    DOI: 10.1520/STP42346S